I use a factory mainspring with a 10# rebound spring for range guns or an 11# rebound spring for combat guns. I've never experienced a "lazy return" with either of them and think this may be from another problem then the springs, namely friction. I can outshoot the 10# springs if I'm not careful though, so that is why they aren't on my duty guns.

I don't understand the "matching" comments about the mainspring and rebound springs. They aren't working together when they are returning to position and as long as the hammer gets back faster than the trigger there should be no problem.